1. Field of the Invention
The present invention relates to an information processing apparatus and method, a recording medium, and a program. More particularly, the present invention relates to an information processing apparatus and method, a recording medium, and a program in which information can be transmitted or received more reliably while ensuring real-time characteristics without decreasing transmission efficiency.
2. Description of the Related Art
Generally, in packet communication in a communication line in which the risk of packet transmission errors and packet loss is high, in order to maintain the reliability of the contents of the communication, an automatic repeat request (ARQ) method is often used.
In this ARQ method, as is disclosed in Japanese Unexamined Patent Application Publication No. 11-284607, when the transmission side transmits a packet and, thereafter, receives a notification from the receiving side indicating that the transmitted packet is received, the transmission side transmits the next packet. However, when the transmission side cannot receive a notification from the receiving side indicating that the transmitted packet is received, the transmission side repeats the process of retransmitting the same packet.
This ARQ method ensures the reliability of packet distribution in communication and is a method suitable for bulk data distribution of electronic mail, a file transfer application, etc., for which the transmitted information needs to be reliably received by the receiving side.
However, according to the ARQ method, when the packet cannot be received by the receiving side, since the operation of retransmitting the same packet is repeated, it is difficult to maintain real-time characteristics.
Furthermore, when an application program which requires real-time characteristics cannot receive a packet via a network even when waiting is performed for a time exceeding a permissible range, assuming that that packet is lost, it is necessary to process packets which follow. However, in the ARQ method, since the packet is retransmitted even in such a case, the retransmission process is performed even for a packet which is determined to exceed the permissible range in the application (receiving side), with the result that a problem arises in that the transmission bandwidth of the network and the memory of the receiving side are wasted.
For this reason, for example, in a wired network with a low error rate such as an optical-fiber network, since reliable packet distribution can be expected, real-time characteristics are ensured by using a protocol, such as UDP (User Datagram Protocol), which does not have a packet retransmission mechanism.
However, since a wireless network has a relatively high data error rate in comparison with a wired network, it is difficult to use a protocol, such as UDP, which does not have reliable packet distribution. Therefore, in a wireless network, lost packets are restored in the receiving side by using an FEC (Forward Error Correction) method capable of restoring packets in the receiving side.
However, in this FEC method, in comparison with the ARQ method, not only is the size of the processing circuit increased, but also error-correction information must be added to the packets. As a result, a problem arises in that redundancy occurs and the transmission efficiency is substantially decreased.